I'm not sure which kind of mods the person above is referencing, but the game code is already very moddable with DnSpy, just because you used Unity Mono, so your game will already be modding-friendly as long as you keep using that engine. I already wrote a hard mod with respawning monsters etc.
The only thing that is difficult is adding new animations and levels, but that is more of a general Unity problem. One thing you coul try is to read AssetBundles from a folder, but it's us who will send you the needed code for it. You focus on the game :)